1. Field of the Invention
The present invention relates to a pump.
2. Background Information
Pumps are typically used to pump fluid through a hydraulic system. There are various types of pumps including positive displacement and variable displacement pumps. Positive displacement pumps typically include a piston(s) that moves in a reciprocating manner to pull fluid into a pumping chamber and pump the fluid out of the chamber. Wobble plate positive displacement pumps have multiple pistons that are coupled to the output shaft of an electric motor by a wobble plate. The wobble plate includes a cam surface that cooperates with a bearing assembly to simultaneously move the pistons within the pumping chambers in a manner to continuously pump fluid from the pump.
Wobble plate pumps contain a diaphragm that seals the pumping chambers of the pump. The diaphragm moves with the reciprocating pistons and thus undergoes a continuous stressing cycle. The stressing cycle can cause fatigue and failure of the diaphragm, resulting in leaking and possibly in-operation of the pump. Some wobble plate pumps have a space between the wobble plate and the outside housing wall of the pump. During certain pumping positions the diaphragm may actually bulge into the space, creating additional stress and shortening the life of the diaphragm.
The bulging effect limits the pressure at which the pump can operate. The operating pressure can be increased by designing a thicker diaphragm or by attaching a reinforcing liner. Unfortunately, increasing the thickness of the diaphragm or bonding a reinforcing liner increases the diaphragm stresses. Selecting the diaphragm thickness always requires a trade off between operating pressure and diaphragm stresses.